Well, I think the statement is quite interesting if you consider that words are reified concepts, in the metaphor, dead wood. Words are, to some degree, ideas that have ossified into a more or less agreed-upon meaning: they've been defined and circulate as a unit of meaning.

I think what this metaphor is getting at is that one cannot build or create new ideas with prefabricated units of meaning. (Of course, one can be quite creative with Legos, which gives me pause.)

Now, there are certainly a thousand objections to this, and it is surely a bit too simplistic. But I think the metaphor neatly sums up the strong (or vulgar) version of the Sapir-Whorf hypothesis, which Benjamin Whorf explained as follows:

"We dissect nature along lines laid down by our native languages. The categories and types that we isolate from the world of phenomena we do not find there because they stare every observer in the face; on the contrary, the world is presented in a kaleidoscopic flux of impressions which has to be organized by our minds—and this means largely by the linguistic systems in our minds. We cut nature up, organize it into concepts, and ascribe significances as we do, largely because we are parties to an agreement to organize it in this way — an agreement that holds throughout our speech community and is codified in the patterns of our language... all observers are not led by the same physical evidence to the same picture of the universe, unless their linguistic backgrounds are similar, or can in some way be calibrated"

In many ways, the language that we receive, into which we are thrust, controls and determines what we can say, and necessarily, what we can think. This is simplistically referred to as the concept of the "prisonhouse of language," but I think it's undeniable that there's some validity to the theory.